Wire coating composition



Patented Aug. 24, 1954 UNITED STATES WIRE COATING COMPOSITION ofDelaware N Drawing. Application December 29, 1951, Serial No. 264,225

4 Claims.

7 1 This invention relates to an improved wire coating composition foruse in making insulated magnet wire of the enameled magnet wire type.The invention further contemplates the provision of an improved magnetwire made by applying to a metallic conductor a thin film of the.

new coating composition. This invention is a continuation-impart of myapplication Serial No. 76,661, filed February 15, 1949, now Patent No.2,570,476, dated October 9, 1951.

In my aforesaid patent, I have described and claimed a wire coatingcomposition that sets by gelation consisting essentially of a celluloseester of one or more aliphatic acids containing from 2 to 4 carbonatoms, dissolved in a solvent composed essentially of 15% to of a lowermonohydroxy alkanol, to 60% of benzene or one or more of itsmethylhomologues, and 10% to 30% of a lower dialkyl ketone. The amount ofester employed in this coating composition in relation to the amount ofsolvent is sufficient to impart to the composition a viscosity in therange of 600 to 1500 centipoises at a temperature of 100 F., but in anyevent is not less than about 12% by weight of the composition. It ischaracteristic of the composition that it sets to a nonflowing solid bygelation upon being cooled to room temperature,- say, about 60 F.-,without solvent evaporation being necessary for such solidification tooccur.

The aforesaid coating composition has the advantage that a single coatapplied to a wire, in an operation involving drawing the wire through abath of the composition at a temperature above its gelation temperature,sufiices to form on the wire a coating of adequate thickness to meet thedielectric requirements of wire coating compositions as generallyapplied to magnet wires; and furthermore, the prolonged baking operationthat is a necessary part of making conventional enameled magnet wires iseliminated. Wires may be coated with gelable coating composition at muchhigher rates of wire travel through the coating bath than is possiblewith conventional wire enamels. However, a disadvantage of the coatingcomposition of my aforesaid application is that for some purposes itsresistance to abrasion is undesirably low. For this reason, wires coatedwith the composition of my aforesaid patent have many opportunities foruse in structures where abrasion resistance of the wire coating is ofmarked importance, as, for example, in motor. coils where the coils mustbe forced into slots in which they fit tightly.

I have discovered that the abrasion resistance of insulating coatingsformed on magnet wire by a gelable lacquer coating composition of thecharacter described in my aforementioned patent can be very muchincreased by incorporating in the lacquer composition a minor proportionof a resinous condensation polymer of the oxidizing alkyd resin typetogether with a minor proportion of a thermosetting resinouscondensation polymer of the urea formaldehyde type. Based on thisdiscovery, the present invention provides a wire coating compositionconsisting essentially of a solute composed essentially of (a) to byweight of a cellulose ester of at least one aliphatic acid containing 2to 4 carbon atoms (e. g. cellulose acetate butyrate), (b) 5% to 30% byWeight of a resinous condensation polymer with a lower aliphaticaldehyde of a substance selected from the group consisting of urea,thiourea, cyanamide, guanidine, and melamine (e. g. a urea formaldehydepolymeric resin), and (c) 5% to 20% by weight of a drying-oilmoolifiedresinous condensation polymer of a polyhydric alcohol and a substanceselected from the group consisting of polybasic acids and theiranhydrides, the oil content of said oil-modified polymer being in therange from 30% to 50% by weight thereof (e. g. a resinous. polymer ofphthalic anhydride and a polyhydric alcohol, modified with 40% by weightof soy-bean oil), the said solute being dissolved in a solvent composedessentially of approximately 1 part by weight of a lower monohydroxyalkanol, 3 parts by weight of a substance selected from the groupconsisting of benzene and its methylhomologues, and. 1 part by Weight ofa lower dialkyl ketone (how'- ever, thoroughly satisfactory coatingcompositions may be made in which the proportions of the solventconstituents differ substantially from those given). The proportions ofsolute to solvent in the coating composition are such as to yield alacquer which is fluid at temperatures above, say, R, but which gels toa non-flowing solid at or near room temperature, say, about 65 F. Forbest results the proportions of solute to solvent is in the range from1:10 to 1:6, 1. e. the solute constitutes 10% to 17% by weightpf thecomposition, and in any event is sufficient to impart to the compositiona viscosity at 100 F. in the range from 600 to 1500 centipoises.Generally it is desirable, but it is not essential, to incorporate inthe lacquer composition one or more chemically inert pigments oropaquing agents, which ingredients may be employed in the proportions.of about 3% to 10% by weight of the solute composition. Otheringredients which a mixture of a thermosetting urea formaldehyde type ofresin and an oil-modified oxidizing alkyd resin. The solvent compositionis indeed that of my said patent, and here, as in that patent, I use alower monohydroxy alkanol boiling at a temperature of about 100 C. orless at atmospheric pressure. I may, of course, also use low boilingcommercial alcohol-base solvents such as the one composed of about 92%commercial ethyl alcohol, about 4.8 methyl alcohol, about 1.4% methylisobutyl ketone, about 1% ethyl acetate, and about 1% hexane mentionedin my aforementioned patent. The particular solvent material as notedabove and as set forth in the claims is, of course, broad enought toinclude such monohydroxy alkanols such as the commercial solvent asabove noted. Similarly, I use a lower dialkyl ketone having from 3 to 6carbon atoms and boiling at a temperature of about 100 C. or less atatmospheric pressure.

The cellulose esters that are used in the new lacquer composition arethe same that have been used heretofore indip coating lacquers and inpropionyl, and cellulose acetate butyratecontaining, say, 12 to 18%acetyl and 15% to butyryl.

The thermosetting resin employed in the solute of the coatingcomposition of the present invention is a thermosetting resin such as isformed by condensation of urea, thiourea, cyanamide, guam'dine ormelamine with a lower aliphatic aldehyde (usually an aldehyde containingfrom 1 to 4 carbon atoms, and most commonly formaldehyde), or with suchan aldehyde and an alcohol, e. g., butanol. Such resin may beincorporated in the lacquer composition either in the unpolymerized formor as a partially polymerized product. In either case, it is mostadvantageously incorporated in the form of a solution containing, say,to 75% by weight of resin constituents and the balance solvents such asxylol and butanol. In general, I prefer to employ the solutions of thesecondensation polymers which are commercially available. In making up thecomposition from such a solution, the amount of the non-volatile polymerconstituent contained therein is alone taken into account in determiningthe solute proportions of the composition, and the volatile solventconstituents of the polymer solution are taken into account ascomponents of the solvent of the lacquer composition.

Although particularly satisfactory results are obtained by employing aurea formaldehyde condensation polymer or other condensation polymer ofthe character mentioned above in preparing lacquer compositionsaccording to the invention, any thermosetting resin which is compatiblewith the cellulose ester and which can be dissolved in the solventcomponent of the composition may be employed with beneficial results.

The alkyd resin employed in the solute of the new coating composition isof the type known to the trade as a short oil oxidizing alkyd resin, andconstitutes a drying-oil-modified resinous condensation polymer of apolybasic acid or acid anhydride and a polyhydric alcohol in which theoil content is in the range from 30% to 50% by weight. Typically it isprepared by reacting the polybasic acid or acid anhydride, such asphthalic, maleic, fumaric or carbic acid or anhydride with glycerol, aglycol, pentaerythritol, or other polyhydric alcohol and with the dryingoil (e. g. linseed oil, dehydrated castor oil, soybean oil, China woodoil, oiticica oil, or a fish oil) in the presence of a catalyst. Perhapsthe most satisfactory of these resins is the glyceryl phthalate polymerprepared by reaction of phthalic anhydride with glycerol and soy-bean orequivalent drying oil. The alkyd resin is most advantageouslyincorporated in the lacquer composition in the form of a solutioncontaining, say, 50% to by weight of the alkyd resin constituent and thebalance solvents such as xylol, toluol, or mineral spirits. In general Iprefer to employ the solutions of these oil-modified condensationpolymers which are commercially available. In making up the compositionfrom such solutions, the amount of the nonvolatile polymer constituenttherein is alone taken into account in determining the soluteproportions of the composition, and the volatile solvent constituents ofthe polymer solution are taken into account as components of the solventof the lacquer composition.

Following is an example of a typical wire coating composition preparedin accordance with this invention:

Ingredient Percent Titanium dioxide 0. 7 0. 6 Mixed lower monohydroxyalkanols (mostly ethyl alcohol) 24. 4 l9. 7

In this composition, the solids constitute 16.8 parts by weight, or13.5% by weight of the composition, and the solvent componentsconstitute 107.4 parts by weight, or 86.5% by weight of the composition.This composition has a viscosity of about 1000 to 1200 centipoises at F.and solidifies by gelation when cooled to a temperature of about 65 F.

Coating compositions prepared in accordance with the invention are mostadvantageously applied to wires by the method described and claimed inUnited States Patent No. 2,547,047 to Harry L. Saums, John H. Vail andHoward W. Sturgis, using apparatus of the character described andclaimed in United States Patent No. 2,558,993 to Howard W. Sturgis andEmil H. Olson. Briefly, the method of applying the coating compositionto the wire involves passing the wire into a bath of the compositionmaintained at a temperature well above its gelation temperature, andthen withdrawing the wire with a film of the coating compositionadhering thereto. This film cools almost at once as the wire emergesinto the room atmosphere to below its gelation temperature and therebysets almost immediately to a non-flowing solid film. Eventually thevolatile constituents of the gelled film evaporate, leaving a wirecoated with an intimate blend of the non-volatile constituents of thelacquer. The

finished wirethus comprises a metallic .conductor having thereon athin'substantially uniform and continuous coatingcomposed essentially of(a) 60% to 85% by weight of a cellulose ester .of at least one aliphaticaciducontaining 2 to 4 carbon atoms (e. g. cellulose acetate butyrate),intimately blended with (b) 5% to 30% by weight of a resinouscondensation polymers-of .a lower aliphatic aldehyde with .a substanceselected from the group consisting of urea, thiourea, cyanamide,guanidine, and melamine (e. gsurea formaldehyde resin), and (c) 5% to20% by weight of an'oxidized drying-oil-modified alkyd resin.

It is a major advantage of coating compositions prepared in accordancewiththeinventionthat the insulating film formed by its use on thesurface of the wire is substantially continuous with but very few andwidely separated pinholes even when the coating is applied at a highrate of wire travel. Also, the coating is uniform in thickness about theperiphery of the wire and along its length, and, most important, it istightly adherent to the wire and highly resistant to abrasion.

The remarkably improved characteristics of wire coated with thecomposition of this invention, in comparison with a Wire coated with agelable lacquer prepared in accordance with my aforementioned patent, isillustrated by the test results summarized in Table I. In each of the 1tests mentioned, the wire designated as wire A Table I Wire A Wire BScrape Test (wire aged 1 week) 13.0 6. 0 Continuity Test 1 2. 0 7. 3Abrasion TestA (wire aged 1 day) 1 936.0 40. 0 Abrasion Test B (Wireaged 1 month) 2, 795. 0 333.0

1 Figures given for these tests are averages of three separatedeterminations.

The manner in which the tests reported in the table were carried out isas follows:

Scrape test.The so-called Delco scrape test was used in obtaining thedata given in the table. In this test the wire is pulled horizontallyunder the point of a needle, the needle being mounted so that it bearson the wire with a weight that can be varied. The needle and the wireare connected together in a low-voltage electrical circuit. The weight(in ounces) on the needle which is just sufiicient to cause the needleto scrape through the coating on the wire and complete the electriccircuit is taken as an index of the scrape resistance of the wire. Thegreater the weight with which the needle must be loaded, the better isthe quality of the coating insofar as regards its scrape resistance.

Continuity test-To determine the continuity of a coating film on a wire,the coated wire is drawn through a pool of mercury. The wire and themercury are connected together in an electric circuit which is completedwhenever the 6 mercury. comes in direct contact with the metal of thewire through a perforation in the coating. The number of timesthecircuit is thus completed per hundred feet of wire drawn through themercury pool is taken as an. index of film continuity. The smaller thenumber of such circuit completion, the better is the quality of the.wire.

Abrasion test.-The abrasion resistance of the coating compositionsasgiven in the above table was determined by the use of an apparatuscomprising twelve spokes, each mie-quarter inch in diameter and arrangedin the form of a cylindrical cage, mounted for. rotation about ahorizontal axis. The wire to be tested :is anchored at one end, and theother end is passed over the spokes, being held down againstthe spokesby a weight attached to its otherend. Themetallic conductor of the wireand thespokes of the cage are connected together in an-electricalcircuitand the cage is rotated so that each spoke rubs alongthe coating on thewire with each revolution of the cage.- When the spokes have wornthrough the coating and make contact with the metallic conductor, anelectrical circuit which stops the apparatus is completed. The number ofrevolutions which the cage makes until such circuit is completed is anindex of the resistance of the wire to abrasion. The greater the numberof rotations which the cage makes before the circuit is completed, thegreater is the abrasion resistance of the coating.

It will be noted from Table I above that wire A, made in accordance withthe present invention, was greatly superior in scrape resistance and inabrasion resistance to wire B, prepared using the best gelable lacquerwire coating composition heretofore known. Even in the continuity test,the wire showed marked improvement over the wire made by the method ofmy aforementioned patent. These outstanding test results are indicativeof the wide range of usefulness under conditions imposing substantialabuse on the insulating coating of wire made in accordance with thisinvention.

I claim:

1. A Wire coating composition consisting essentially of a solutecomposed essentially of (a) 60% to by weight of a cellulose ester of atleast one aliphatic acid containing from 2 to 4 carbon atoms, (b) 5% to30% by weight of a resinous condensation polymer of a lower aliphaticaldehyde with a substance selected from the group consisting of urea,thiourea, cyanamide, guanidine, and melamine, and (c) 5% to 20% byweight of a drying-oil-modified resinous condensation polymer of apolyhydric alcohol and a substance selected from the group consisting ofpolybasic acids and their anhydrides, the oil content of saidoil-modified polymer being in the range from 30% to 50% by weightthereof, said solute being dissolved in a solvent composed essentiallyof approximately 1 part by weight of a lower monohydroxy alkanolcontaining 1-5 carbon atoms and having a boiling point of about 0., 3parts by weight of a substance selected from the group consisting ofbenzene and its methyl homologues, and 1 part by weight of a lowerdialkyl ketone containing 3-6 carbon atoms and having a boiling point ofabout 100 C., said composition having a viscosity in the range from 600to 1500 centipoises at 100 F. and gelling to a non-flowing solid atabout 65 F.

2. A wire coating composition consisting essentially of a solutecomposed essentially of (a) 60% to 85% by Weight of cellulose acetatebutyrate, (b) to 30% by weight of a resinous condensation polymer ofurea and formaldehyde, and (c) 5% to by weight of a drying-oilmodifiedresinous condensation polymer of a polyhydric alcohol with phthalicanhydride, said solvent being dissolved in a solvent composedessentially of approximately 1 part by weight of a lower monohydroxyalkanol containing 1-5 carbon atoms and having a boiling point of about100 0., 3 parts by weight of a substance selected from the groupconsisting of benzene and its methyl homologues, and 1 part by weight ofa lower dialkyl ketone containing 3-6 carbon atoms and having a boilingpoint of about 100 C., said composition having a viscosity in the rangefrom 600 to 1500 centipoises at 100 F. and gelling to a non-flowingsolid at about 65 F.

3. Magnet wire comprising a metallic conductor having thereon a thinsubstantially uniform and continuous coating composed essentially of (a)60% to 85% by weight of a cellulose ester of at least one aliphatic acidcontaining from 2 to 4 carbon atoms, (b) 5% to by weight of a resinouscondensation polymer of a lower aliphatic aldehyde with a substanceselected from the group consisting of urea, thiourea, cyanamide,guanidine, and melamine, and (c) 5% to 20% by weight of an oxidizeddrying-oil-modified alkyd resin.

4. Magnet wire comprising a metallic conductor having thereon a thinsubstantially uniform and continuous coating composed essentially of (a)to by weight of cellulose acetate butyrate, (b) 5% to 30% by weight of aresinous condensation polymer of urea and formaldehyde, and (c) 5% to20% by weight of an oxidized drying-oil-modified alkyd resin.

References Cited in the file of this patent UNITED STATES PATENTS Number

1. A WIRE COATING COMPOSITION CONSISTING ESSENTIALLY OF A SOLUTECOMPOSED ESSENTIALLY OF (A) 60% TO 85% BY WEIGHT OF A CELLULOSE ESTER OFAT LEAST ONE ALIPHATIC ACID CONTAINING FROM 2 TO 4 CARBON ATOMS, (B) 5%TO 30% BY WEIGHT OF A RESINOUS CONDENSATION POLYMER OF A LOWER ALIPHATICALDEHYDE WITH A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF UREA,THIOUREA, CYANAMIDE, GUANIDINE, AND MELAMINE, AND (C) 5% TO 20% BYWEIGHT OF A DRYING-OIL-MODIFIED RESINOUS CONDENSATION POLYMER OF APOLYHYDRIC ALCOHOL AND SUBSTANCE SELECTED FROM THE GROUP CONSISTING OFPOLYBASIC ACIDS AND THEIR ANHYDRIDES, THE OIL CONTENT OF SAIDOIL-MODIFIED POLYMER BEING IN THE RANGE FROM 30% TO 50% BY WEIGHTTHEREOF, SAID SOLUTE BEING DISSOLVED IN A SOLVENT COMPOSED ESSENTIALLYOF APPROXIMATELY 1 PART BY WEIGHT OF A LOWER MONOHYDROXY ALKANOLCONTAINING 1-5 CARBON ATOMS AND HAVING A BOILING POINT OF ABOUT 100* C.,3 PARTS BY WEIGHT OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OFBENZENE AND ITS METHYL HOMOLOGUES, AND 1 PART BY WEIGHT OF A LOWERDIALKYL KENTONE CONTAINING 3-6 CARBON ATOMS AND HAVING A BOILING POINTOF ABOUT 100* C., SAID COMPOSITION HAVING A VISCOSITY IN THE RANGE FROM600 TO 1500 CENTIPOISES AT 100* F. AND GELLING TO A NON-FLOWING SOLID ATABOUT 65* F.